Production of magnesium metal

ABSTRACT

An improved method for producing magnesium metal comprising: contacting a magnesium halide compound with lime (CaO) and a reducing agent selected from the group consisting of aluminum, aluminum-silicon, aluminum silicide and mixtures thereof at an elevated temperature sufficient to provide a molten reaction mass; conducting the reaction under a low absolute pressure sufficient to volatilize the magnesium metal formed and condensing the magnesium vapors, or conducting the reaction under normal pressures and separating a molten magnesium metal from the molten product reaction mass.

[Muted States Patent 1191 1111 3,849,118 Mod et all. Nov, 19, 1974 1 PRODUCTION OF MAGNESIUM METAL 3,397,056 8/l968 Layne et a1. 75/68 B [75] Inventors: William A. Mod, Lake Jackson; FOREIGN PATENTS OR APPLICATIONS lf EMS, Angleton, both 0f 464,520 4/1937 Great Britain 75/67 [73] Assignee: The Dow Chemical Company, Primary Dewayne Rulledge Midland, Mich. Assistant Examiner-M. J. Andrews [22] F1 d J 15 1970 Attorney, Agent, or Firm-Bruce M. Kanuch 1e une [21] Appl. No.: 48,880 [57] ABSTRACT Related Application Data An improved mfthsd for produciing rlpalgcrjiesium metlag comprising: con ac mg a magnes um a 1 e compou [63] 56352122 of 660217 1967 with lime (C210) and a reducing agent selected from V the group consisting of aluminum, aluminum-silicon, [52] U 5 Cl 75/67 aluminum silicide and mixtures thereof at an elevated [51] In. .0. 45/00 temperature sufficient to provide a molten reaction [58] Field 175/67 mass; conducting the reaction under a low absolute pressure sufficient to volatilize the magnesium metal [56] References Cited formed and condensing the magnesium vapors, or conducting the reaction under normal pressures and UNITED STATES PATENTS separating a molten magnesium metal from the molten 2,184,705 12/1939 Willmore B oduct reaction mass 2,251,968 8/1941 Adamoli 75/67 p 2349.927 5/1944 Arimori et a]. 75/67 5 Clams, N9 Drawmgs PRODUCTION OF MAGNESIUM METAL RELATED APPLICATION This is acontinuation of application Ser. No. 660,217 filed Aug. 14, 1967, now abandoned.

BACKGROUND OF THE INVENTION Magnesium, generally, is now produced commercially by electrolysis of magnesium chloride fused salts in electrolytic cells and by silicothermic and carbothermic reduction of magnesium ores such as, for example, dolomite [CaMg (CO The first method uses electrical power to reduce the magnesium chloride salt while the second generally employs iron and aluminum silicon compounds or carbon to reduce magnesium oxide usually obtained from dolomite.

Electrolytic methods, while advantageous in that magnesium and chlorine are co-produced, require costly installations and considerable electric power. Silicothermic and carbothermic methods which are now employed require high reaction temperatures, low absolute pressures and considerable reaction times, usually in the order of from 1 to hours. 1

, The present invention involves an improved silicothermic reduction method which, by employing se lected reactants, now unexpectedly affords the production of magnesium metal at considerably lower temperatures, with considerably reduced reaction times and with or without the use of low absolute pressures.

SUMMARY OF THE INVENTION In general the present novel invention consists of contacting a magnesium halide compound with lime (CaO) and a reducing agent selected from the group consisting of aluminum, aluminum-silicon, aluminum silicide and mixtures thereof, at a temperature of from about 700C. to about 1 100C. for a sufficient period of time to provide a substantially complete reduction of the magnesium halide to magnesium metal. The maximum quantity of reducing agent employed is that which is about stoichiometrically required to reduce substantially all the magnesium halide present. Lime should be provided in an amount which at the minimum is stoichiometrically required to form a compound with substantially all the free halides released during the process. The resulting magnesium metal is separated from the product reaction mass, either as the molten magnesium metal or as a vapor, and, generally, is cast into ingots.

PREFERRED EMBODIMENTS Usually in practice, a molten bath of magnesium halide containing a reducing agent and lime (CaO) is maintained ata temperature of from about 700 to about 1 100C. at atmospheric pressure for a sufficient period of time to allow a substantially complete reduction of the magnesium halide to magnesium metal. The magnesium metal is separated from the product read tion mass by dipping or pouring off the top of the molten mixture, and is usually cast into ingots. Low absolute pressures sufficient to vaporize the substantially pure magnesium metal at the conditions of the process as defined herein can be employed and the vaporized magnesium can then be separated from the reaction mass and solidified.

The present novel process can be carried out at a temperature range of from about 700C. to about 1100C. A temperature of from about 850 to 1000C. is preferred.

Magnesium halide compounds which may be used in the present novel process are MgF MgCl Mgl MgBr and mixtures thereof. The magnesium halide compound should be anhydrous and anhydrous MgF- is usually preferred because of its availability.

Suitable reducing agents consist of aluminum, aluminumsilicon mixtures, aluminum silicide and mixtures thereof. As indicated previously, the reducing agent is usually employed in amounts, at a maximum, equal to about that stoichiomctrically required to reduce substantially all the magnesium halide in the reaction mass to magnesium metal. Usually the reducing agent is provided in amounts from about per cent to about per cent of that stoichiometrically required. Preferably an excess of lime (CaO) over that stoichiometrically required to combine with substantially all the free halides released during the process is employed in the present novel invention. Generally from about 101 per cent to per cent over that stoichiometrically required is employed.

The reactants are usually introduced into the reaction mass as finely ground matter. Normally, a particle size, at a maximum, of about 100 mesh is appropriate for the magnesium halides, lime (CaO) and reducing agents. Aluminum is usually employed having a larger particle size of about 20 mesh. For ease of handling, the reactants may be introduced into the reaction chamber in the form of premixed compact forms such as, for example, briquets, pellets and the like. This is usually a more convenient form to employ when the reaction is to be carried out under reduced absolute pressures. However, as indicated, the reducing agent can be added to a molten bath of magnesium halide compound or the reactants may be provided in a premixed granular form.

The reaction time associated with the novel process is quite short and usually a reaction time, at the maximum, of about 20 minutes is preferred, as compared with other carbothermic and silicothermic processes which require anywhere from 1 hour to about 20 hours for a complete reaction. A reaction time of from about 10 minutes to 30 minutes usually is employed. The longer reaction times usually are associated with the lower operating temperatures.

When a low absolute pressure is employed, it should be sufficiently low so as to afford the formation of magnesium vapors at the designated temperature ranges. Usually a low absolute pressure of from 10 to about 1000 microns mercury absolute is sufficient, and normally a low pressure absolute of less than about 500 microns is preferred. Lower absolute pressure may be em ployed without detrimentally affecting the novel method as defined herein.

It is apparent that the present novel process affords many advantages over these processes heretofore employed. Substantially pure magnesium metal can now be prepared by employing substantially lower reaction temperatures and substantially shorter reaction times.

The following examples will facilitate a more complete understanding of the present novel process. They are included herein for illustrative purposes only and are not meant to limit the present invention to the specific embodiments incorporated therein.

EXAMPLE 1 The following were blended in a Vblender for 15 minutes.

Lime 100 mesh 12.48 grams MgF 100 mesh 8.20 grams Si 100 mesh 3.70 grams Al 20 mesh 2.37 grams TOTAL 25.75 grams The mixture was compressed at 5 tons per square inch into the form of a l-inch diameter briquet. After compression, the briquet weighed 26.75 grams. The briquet was placed in a graphite crucible. This in turn was placed in a vacuum furnace equipped with a Vycor condenser sleeve. The chamber was placed under reduced absolute pressure of 500 microns. The briquet was heated by means of an induction furnace using the graphite crucible as the susceptor. A film of metal started to form on the sleeve when a temperature of 750800C. was reached. The temperature was raised to 1100C. and maintained for 20 minutes while the vacuum ranged from 500 to 1000 microns. The reaction chamber was allowed to cool under vacuum. The briquet was weighed and was found to have lost 2.61 grams.

The Vycor sleeve was weighed before and after the reaction and was found to have picked up 2.2 grams of metal. Two layers were observed on the Vycor condenser sleeve. The layers were removed and analyzed by X-ray diffraction and emission spectroscopy. The thin layer next to the crucible had the following analysis:

X-ray Al, MgF

Emission Spec. Al chief constituent Mg heavy Ca 0.77%

The dense layer had the following analysis:

Mg only Mg chief constituent Al 5% (weight per cent) Ca 0.0 T8 7? Xray Emission spec.

EXAMPLE 2 MgF 100 mesh, lime -100 mesh, Si -l00 mesh, and A1 20 mesh, were mixed for approximately minutes in a V-blender. A l-inch diameter briquet was made from the mixture at 5 tons per square inch. The

briquet had the following composition:

Lime 11.54 grams MgF 8.19 grams Si 3.69 grams Al 2.36 grams TOTAL 25.78 grams Vycor sleeve showed a weight pick-up of 1.20 grams. Mg in the initial briquet was 3.2 grams.

The per cent Mg recovered 1.20/3.20 X 37.5 percent. Emission spectrographic analysis of the magnesium metal was as follows:

Si .0()8% Ca .004% Al 24% Mn 002% Fe .0()4% Cu 00 1 "/1 Ni non-delectcd Mg balance EXAMPLE 3 lvlgF 100 mesh, lime 100 mesh, and Al 20 mesh were mixed for approximately 15 minutes in a V-blendcr. A l-inch diameter briquet was made from the mixture at 5 tons per square inch. The briquet had the following composition:

Lime 15.56 grams MgF 1082 grams Al 3.12 grams TOTAL 2950 grams The briquet was treated as in Example 1. It was heated to 1000C. and held at this temperature for 20 minutes. The pressure ranged from 19 to 50 microns. At 900C magnesium started to condense on a Vycor sleeve.

The weight loss by briquet was 2.4 grams. The weight pickup by Vycor sleeve was 2.3 grams.

The Mg in the initial briquet was 4.22 grams.

The per cent Mg recovered 2.3/4.22 X 100 54.5 percent. Emission spectrographic analysis of the magnesium metal was as follows:

Si 0.015% Ca 0.048%

A1 0.004% Mn 0.002% Fe 0.001% Cu 0.00057r Ni non-detected Mg balance Various modifications may be made in the present novel process without departing from the spirit or scope thereof for it is understood that we limit ourselves only as defined in the appended claims.

What is claimed is:

1. A process for preparing magnesium metal which comprises:

a. contacting at atmospheric pressure a magnesium halide compound with lime and a reducing agent selected from the group consisting of aluminum, aluminum-silicon compounds, aluminum silicides and mixtures thereof, at a temperature within a range of from about 700C to about 1 100C for a sufficient period of time to reduce at least a portion of the magnesium halide to form molten magnesium metal, said lime being provided in an amount which at the minimum is stoichiometrically required to react with substantially all halides released from said magnesium halide during the reaction, and

b. recovering said molten magnesium metal.

3,849,1 l8 6 2. The process of claim 1 wherein said magnesium halide is magnesium iodide. halide is magnesium fluoride.

3. The process of claim 1 wherein said magnesium halide is magnesium chloride. hahde magneslum bromlde' 4. The process of claim 1 wherein said magnesium 5 5. The process of claim 1 wherein said magnesium 

1. A PROCESS FOR PREPARING MAGNESIUM METAL WHICH COMPRISES: A. CONTACTING AT ATMOSPHERIC PRESSURE A MAGNESIUM HALIDE COMPOUND WITH LIME AND A REDUCING AGENT SELECTED FROM THE GROUP CONSISTING OF ALUMINUM, ALUMINUM-SILICON CMPOUNDS, ALUMINUM SILICIDES AND MIXTURE THEREOF, AT A TEMPERATURE WITHIN A RANGE OF FROM ABOUT 700*C TO ABOUT 1100*C FOR A SUFFICIENT PERIOD OF TIME TO REDUCE AT LEAST A PORTION OFF THE MAGNESIUM HALIDE TO FORM MOLTEN MAGNESIUM METAL, SAID LIME BEING PROVIDED IN AN AMOUNT WHICH AT THE MINIMUM IS STOICHIOMETRICALLY REQUIRED TO REACT WITH SUBSTANTIALLY ALL HALIDES RELASED FROM SAID MAGNESIUM HALIDE DURING THE REACTION, AND B. RECOVERING SAID MOLTEN MAGNESIUM METAL.
 2. The process of claim 1 wherein said magnesium halide is magnesium fluoride.
 3. The process of claim 1 wherein said magnesium halide is magnesium chloride.
 4. The process of claim 1 wherein said magnesium halide is magnesium iodide.
 5. The process of claim 1 wherein said magnesium halide is magnesium bromide. 